Process of reducing aluminium



(No Model.) a SheetS -Sheet 1.

F. A. eoooHf & L. WALDD. PROGESS'OF REDUCING ALUMINIITM.

No. 528,365- V -P atented ,0c t. 30, 1894. I

FRANK A. eooon, or NEW HAVEN, AND'LEONARD WALDO, F BRIDGE- ron'r, oonuncricur; SAID \WALDO ASSIGNOR TO THE wALDo FOUN- DRY, or NEW JERSEY EROGESS OF'REDUCING ALUMINIUM.

SPECIEIQATION forming part of Letters Patent No. 528,365, dated. October 30, 1894. Application tiled September 1', 1893. Serial No. 484,561. (No specimens.)

' ducing Aluminium; and we do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

The invention described herein relates to processes for the reduction of aluminium from its compounds by the electrolysis of a suitable fused mass containing such compounds. The compound of aluminium used should be one which will fuse at a temperature and under conditions which shall be practically attainable.

More especially our invention herein described relates to the reduction of aluminium from its chloride.

In the accompanying drawings, which are hereby made a part of this specification, is shown one form of apparatuss'uitable to the practice of our invention. dVedo not, however, limit ourselves to the apparatus shown, since any other suitable apparatus'jwould answer equally well for the practice of our invention.

Figure 1 represents a sectional diagrammatic view of the apparatus employed by us; Fig. 2 represents a sectional view of a modified form of apparatus employed by us. Fig..

3 represents a sectional diagrammatic view of another modified form of apparatus employed byus.

Similarletters refer to similar parts th roughont thedrawings. My

h is a furnace having a fire boxYf, and openingf in the top of the furnace, nto which is set a tapering crucible A, the same being supported by the sides of the opening f. The construction of the crucible and thcarrangomcnt of the electrodes and conductors are hereinafter-fully described. I

'l is a tank from which thohydrogcn is supproper'proportions, the chlorideof aluminium and the chloride of an alkaline metal (prob erably sodium) or of an alkaline earth metal,

with the fluoride of aluminium and the fluoride of sodium; A convenient way to form a suitable bath is to combine the double chloride of aluminium and sodium (represented by the formula 2NaGl.Al,,Cl with the mineral cryolite. We find it of advantage to add to the combination just named an additional amount of chloride of sodium in excess of the amount necessary to form the double chloride. These ingredients are preferably mingled together in the following proportions:

the double chloride oflalumi nium and sodium, fifteen parts; cryolite, fifty-five parts; sodium chloride thirty parts; buttheseproportionsare variable serviceablywithinwide limits, without in ateri'ally affecting the operation or f unction of the bath, as, in fact, any proportions 'which may be found suitable may be employed.

The reason for employing c'ryolite or the fluorides of aluminium and sodium in the bath is the well known fact that, when they are present and reduction by-th'e action of the electric current takes place, the aluminium melts and flows to globules, while, when the bath contains only the chlorides named, the aluminium is obtained in th'e'form of a powder, which has to be further treated before it can be made commercially available. The object of adding the excess of sodium chloride to the bath is to make the bath more liquid. It is also advantageous iirdiliiting the cryolite. It is not, however, essential to our invention that the excess of sodium chlo ride should be present; nor that the cryolite, or (luoridos of aluminium and sodium should form part of the bath, when the chlorides already mentioned are present.

'2 i eceece Instead of forming the double chloride of ziluininium nnd sodium separately and then addingit toihe both, it will he suiilcient; to place the chloride of aluminium (represented hy ihe forniulr. Alfih} in the both, end then to add the chloride of sodium in such quzm tity that; poi-110i it may unite chemically Willi the chloride of aluminium i0 form the double chloride, While the remainder forms the can cess of sodium chloride needed for the both above described; or the order of introduc tion may be reversed, the former being added first. Usually this order will he found prefcrnblc, astiie chloride of illllll'llillillll is very I5 vole/rile until brought in contact with the so dium chloride.

In place of the cxcess'of sodium chloride or of a part oi? such excess, we may employ s. certain proportion of chloride of potassium, (which is useful in making the both more fluid,) or of some other of the nllmlino n1ei2- nls. In case of any such substitution in the ingredients of the both, the proportions of oil the ingredients used are suitably readjustcd if necessary. For exmnple, ii the chloride of potassium he used, in place of o. port of the sodium chloride, the ingredieni'e ere preferably-mingled togcthor in the fol.- lowing proportions: cryolite, fiftiydve ports; chloride of aluminium,hvolyepnris; chloride of sodium, nineteen ports; chloride of police .Elllllll, fourteen ports; but with a both constituted as last above described, the proporflions given are variable servioeeoly Wit-hie con- 5 siderahle limits withoui materially affecting thc operzitiou or function of the birth, as, in foot, any proportions which may he found suitable may be employed. The crucible ll, preferably employed by us 40 in'the operation of ourinventiou, consists of e tank of iron lined with con] pucced carbon. The carbon .iining L of this tenlr serves as the cathode, the iron of the tank being con-- nectcd by the conductor N with. the negative 5 pole of a. dynamo electric mechine or other suitable source of electricity, 0. The nnodc 0 is 'a detached carbon electrode purtiully immersed in the loath ll; and connector]. in the following manner with the source of nice trinity: We preferably suspend. the enode from an iron bar I) raised above the crucihle and rooting on wooden supports E The bar, D is connected hy the conduoior 5i. to the posiiivc pole of the source of electricity. Ii desircdflho cathode also be formed of detached carbon, suspended in a. similar way to that just; described for ihe anode, orotlierwise supported, end per'i-inlly immersed in a the both E. If desired, a number of sour. "eic 6o carbons may he used to form electrodes as shown in Fig. 2,, Where C 0*, U, and C all suspended from the bar Dcollcctively form the anode. The relative euperficiel areas of the electrodes in any partiouler case .135 are adjusted so as to secure the greatest economy in notion. In place oi. a. carbon anode, an anode of any other suitable mmteriel, as of platinum. may he used. The bath my he liused, aindthe fusion may be mainly mined 'by the application of heat from any suitable source, as from a furnace F. The iempcmiure required to fuse the bath sup,- gestcri above is that of a dull red heat. We may also fuse the ingredients of the bath in :5 separate apparatus and introduce the same in a molten condition into the both at the beginning of the process, the fusion being thereafter maintained in any suitable Way. When the electric current is passed through the both and electrolysis takes place, eluminlurn is deposited at the cathode and the halogens (chiefly chlorine) are liberated at the mod 0. his Well known'thut these gases, inn free state, are highly noxious to health: On this account, and for the further reason that they attack and quickly destroy the positive electrode in the epperetus need in any process similar to the one described, their escape in n. free state would render such process commercially useless. 'lo obviate these diilicultics, and to accomplish other desiruhlc results, We introduce hydrogen into the both. The hydrogen isprefernbly delivered in, a substnntinlly continuous supply underneath the surface of the fused mess in near proximity to or through the anode. In thelattcr' case a longitudinally perforated carbon red C is preterohly employed for the anode, and the.

gas is passed through the some as through a pipe, the gun being supplied through a tube ii connecting With the upper end of the anode l), which may project above the burl). The

hydrogen niuy also if preferred be conducted through u. concrete pipe as the pipe M in Fig. 2. i l hen the halogen elements are liberated by the electrol sis of the both, they combine instantly with ihehydrogen and escope at the anode in iheform of hydrochloric acid or hydrofluoric acid, chiefly the former. These gases in the quantities evolved in our process, ore easily controlled and disposed of, withouhiujury. to apparatus or workmemhy nppropriuiemcuus external to the bath,-as

by the ceo of a. line K, having a strong draft,

end provided with a. hood J, projecting over the crucible A; or cloths or other absorblog" out medic, sexurntecl with Waterway be sue-a.

pended over the crucihle,.the escaping gases being when up hy lhewuier, whose powerof noting no a. solvent for hydrochloric acid and hydrofluoric acid is well knori'n'. Such on arrangement is shown in Fig. 3, Where a represents en endless band or apron of cloth or other suiiehle fehric,,pncsiug over drums m, is attached to shafts b, h. The shaft 1) revolves in journal boxes c and is supported in any suiinbie manner, as by a strip e.'"suspended ifroin rho cei iiug. The Shaft. 12, 1e volvee inhoxes e formed on thecdg'es of the cough if The shufte and hand or apron a are kept in revolution in thedirection indicated by the arrows by power from any suitable source transmitted by the belt (1, passing over the pulley c, which is rigidly attached to the shaft b. The shaft 1) is hung somewhat higher than the shaft h. The drum m on shaft h runs close to or under the surface of water 10 contained in'a shallow pan or trough k, having suitable support Z. The band or apron a being inclined passes through .the water w at the lower side of, the drum m and is thus kept saturated with water. Thus saturated it passes continuously over the crucible.

We do not claim the particular arrangement of devices just described, nor regard it asnoveh-n'or-dowe confine ourselves to the particular devices shown, since any other spitable means external to the bath-might be employed for disposing of the escaping gases.

We preferably'suppl y hydrogen to the bath in excess of the amount required to combine with the halogen elements. The excess of hydrogen substantially permeates the fused mass, thereby securing a more uniform inter-mixture of the ingredients of the bath and protecting the surface of the molten mass from atmospheric action.

In the practical operation of our invention, where we use the suggested baths composed of the chlorides of aluminium and sodium and the fluorides of aluminium and sodium, with or without an excess of chloride of sodium and with or without the chloride of some other alkaline metal, and wither with out the chloride of potassium we have found 'that'we obtain'at the anode hydrochloric acid almost exclusively, with very little trace of fluorine. This shows that the aluminium deposited at the cathode is derived chiefly from the chloride of aluminium in the bath; andwe have found that, bythe occasional addition of chloride" of aluminium (M 01 in snllicient quantities, the bath will be replenished and the process will bea substantially continuous one during a considerable period of time An excess of the chloride of alumini mproduces no injurious eilt'ect, as it is g *dual'ly utilized in the subsequent operation of the process. We have hereinbefore spoken of fluorine being set free, though we are aware that it is considered very diilicult to isolate this element. We, however, use the term fluorine merely for convenience, meaning thereby to include not only free fluorine, if any be liberated, but also any compound thereof, which might be set free at the anode, if hydrogen were not supplied to the bath. As before stated, the aluminium is deposited at the cathode, where it melts forming glolr,

ules, which, when either of the suggested baths whose proportions are hcreinboforo stated, is employed, gather at the-bottom ol the bath, the aluminium having a higher specific gravity than the [used bath. The aluminium may then be removed in any suitable manner as by means ofa ladle lined and covered with carbon, or by drawing it off at the bottom througha suitable opening; or the bath may bepoured out, and,,after being cooled, the-aluminium may be picked out. In case a bath should be used whose specific gravity is higherthan that of aluminium, the aluminium would rise to the top, where it could be easily removed.

In the process herein described, we use an electric current of suitably 10w electro-rno'tive force, usually of from four to ten volts; but the voltage of the current employed will depend on the form and size of the electrodes as well as on the composition of -the bath, it'

being only necessary to have'a voltage sufiicient to decompose electrolytically the chloride of aluminium in the bath under all the existing conditions of resistance, and of chemical constitution.

The electric current which we employ in our process, and which is herein referred to as being passed through the bath,is employed solelyfor purposes of electrolysis. The hydrogen may in the first instance be intro-' ducedbefore or after the electric current is passed through the bath or simultaneously therewith, the order of operations being unimportant.

\Ve are aware that hydrogen has been employed heretofore in processes for reducing aluminium, either as the sole agent or as an auxiliary agent in accomplishing the reduction of the metal from the aluminium compounds used. In the process herein described, we do not employ hydrogenas an agent in such reduction, nor do we in this application claim any process in which hydrogen is so employed.

The objects of introducing hydrogen into the bath in our improved process herein described are, to secure a more uniform inter mixture of the ingredients of the bath, and to protect the Surface of illOdtlOliOll mass from atmospheric action, to protect the anodes from the corrosive action of the halogens set free by the electrolysis of the bath, and to convert such free halogens into amore manageable form.

We do not herein specifically claim these forms of the herein described process which are specifically set forth and claimed in our Ire application, Serial No. 50*,763, filed March 23, 189 l, the same being a divisional application ofthis case.

llaving described our invention, what we claim, and desire to secure by Letters Patent, is--- i. As an improvement in the art of manufacturing aluminium, the herein described process which consists in forming a bath byv fusing together the chlorides of aluminium and sodium and the chloride of another alka: line metal, with the fluorides of aluminium and sodium, passing an electric current te the bath, substantially as and for the putposes set forth.

' FRANK A. (30001;. LEGNARD WALDO.

Witnesses as to Frank A. Gnoch:

SAMUEL E. W n-mm, ANNIE G. WYMAN.

Witnesses as to Leonard Waldo FRANK L. GRANFORD, GILBERT Il. CRAWFORD. 

